Known in the art are dry film photosensitive resists which are a flexible laminated structure consisting of three layers of which the first is a transparent polymer film transmitting UV radiation and having a thickness of 5-100.mu.; the second of said layers is a light-sensitive layer having a thickness of 5-1,000.mu. and comprising a combination of a carboxyl-containing polymer-thickener, a polar oligomer, and a monomeric substance having a boiling point above 200.degree. C. at 760 mm Hg; the third of the layers is a film from a polymeric substance having a thickness of 5-100.mu. and being protective for said light-sensitive layer and disposed thereon.
In one of the known dry film photosensitive resists a light-sensitive layer contains as a carboxyl-containing polymer-thickener a water insoluble copolymer of methylmethacrylate with 10 mol.% of methacrylic acid, as a monomeric substance and a polar oligomer pentaerythritol triacrylate is used. The light-sensitive layer also contains additives of photoinitiators of radical polymerization or a mixture thereof, inhibitors of radical thermopolymerization, dyes, and placticizers.
The use of pentaerythritol triacrylate in combination with the above-cited polymer-thickener makes it possible to obtain dry film photosensitive resists possessing a satisfactory spectrum of properties including stability in galvanic electrolytes.
However, qualitative development of such dry film photosensitive resists is impossible when aqueous developers are used containing no organic substances. For developing the above-cited photosensitive resists, considerable amounts (up to 10 vol.% and more) of organic solvents are usually introduced into the developer, such as butyl cellosolve, as well as surfactants, usually non-ionogenic.
Organic substances contained in the developer are rather difficult to remove from the spent developer; therefore, when the above-cited dry film photosensitive resists are used, environmental contamination takes place, which, under the conditions of mass production, may present a serious ecological problem.
The development of dry film photosensitive resists with aqueous solutions containing no organic substances becomes possible when the acidity of the carboxyl-containing polymer-thickener is increased. For example, if a copolymer of methylmethacrylate with 35 mol.% methacrylic acid is used as a polymer-thickener and pentaerythritol triacrylate as a monomeric substance, the light-sensitive layer is well developed with a 1% aqueous solution of sodium carbonate without the addition of organic solvents. But in this case the chemical stability of the photosensitive resist decreases considerably.
When pentaerythritol triacrylate is replaced by less hydrophilic and, consequently, more stable in aggressive media, monomeric substances, such as pentaerythritol tetraacrylate or trimethylolpropane trimethylacrylate, the chemical stability of the photosensitive resist can be increased. However, this is accompanied by deterioration of the compatibility of the light-sensitive layer components and by instability of adhesion of the light-sensitive layer to the substrate, where the photosensitive resist is applied, especially after prolonged storage.
Thus, because of the above-mentioned disadvantages, the field of application of the known dry film photosensitive resists is limited.